Print warnings at configuration time? Build time?

[Ethan M. <merritt@u.washington.edu>]

Bernhard Simon has reported a problem with "make check"
run under an older version of AIX.  The stringvar demo
caused a segfault. He obligingly traced it to a buffer
overflow from a code path using sprintf, which we use
only if the system does not provide snprintf. We handle
the test case correctly if snprintf is present.

This is a general problem, and is mentioned in our TODO
file but not in the README or INSTALL files.

Simple test
===========
  manually edit config.h to #undef HAVE_SNPRINTF
  build gnuplot
  run test input
	set format xy "%4096g"
	plot x

With snprintf:
   util.c:595: Warning: too many digits for format
Without snprintf:
   *** glibc detected *** realloc(): invalid next size: 0x085c64c8 ***
   Abort
or (different test machine):
   segfault


Question
========

Should we have ./configure print out a warning if snprintf is not found?

WARNING:  Could not find a working snprintf() function.
	  Buffer overflows and segfaults may be triggered by
	  overlong format specifiers provided to gnuplot by the user.
	  Please consider providing snprintf via an external library.

Should we issue the same warning at build time?  Run time?

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle WA